Many electronic devices such as computers, cellular phones, radios, printers, and personal digital assistants use an alternating current (AC) to direct current (DC) adapter or DC to DC adapter to power the device and charge the device's batteries. For example, an AC to DC adapter (“AC/DC Adapter”. “AC Adapter”, or “Adapter”) plugs into an AC electrical outlet and converts 100-240 volt, 50-60 Hz AC input voltage and current into a DC output voltage and current for use by an electronic device. A DC to DC adapter converts a DC input current of one voltage to a DC output current of another voltage. DC to DC adapters (“DC/DC Adapter”, “DC Adapter” or “Adapter”) are often used to power electronic devices from an accessory connector in a vehicle such as an automobile, boat, or airplane.
Adapter output current and voltage are coupled to an input power rail in the electronic device. For electronic devices having a battery or other energy storage device to supply operating power when an adapter is unavailable, output current and voltage from the battery or energy storage device are also coupled to the input power rail. Other components connected to the input power rail detect the presence of an adapter or battery, convert adapter output voltage and battery output voltage to other voltages used by active systems within the electronic device, and charge the battery.
For conventional power supply circuits, a value for maximum adapter power is generally chosen to be large enough to simultaneously supply the loads from active systems in the electronic device and battery charging. Also, adapters used in conventional power supply circuits generally have an output voltage that is substantially higher than the battery output voltage. For example, in an electronic device with a three-cell lithium-ion battery, the battery output voltage on the input power rail varies between about 9 volts DC (VDC) and about 13.5 VDC, depending on battery charge condition. With a conventional supply power supply circuit, adapter output voltage on the input power rail varies in a range from about 16.8 VDC to about 19 VDC and components connected to the input power rail are rated to withstand about 30 VDC to allow for design margins. The large difference between the output voltage of conventional adapters and battery output voltage affects the cost and size of components connected to the input power rail. Components rated to withstand 30 V are larger and more expensive than components rated for lower voltages. Furthermore, voltage converters and other components operate at lower electrical efficiency from adapter input power compared to battery power when the difference between adapter voltage and battery voltage is large. Lower electrical efficiency causes increased dissipation within the electronic device and affects many system parameters such as component operating temperatures, size and cost of active and passive cooling components, printed circuit board area, and enclosure size and complexity.
Recent efforts have sought to improve conventional power supply circuits by including a power allocation controller in the electronic device to apportion adapter output power between active systems and battery charging. In an exemplary power supply circuit, a power allocation controller reduces battery charging current when power consumed by the electronic device exceeds a fixed allocation limit corresponding to maximum adapter current. In another exemplary power supply circuit, the fixed allocation limit corresponds to maximum adapter power. An allocation controller permits the use of a smaller adapter compared to conventional power supply circuits because the maximum load from active systems and the maximum load from battery charging do not occur concurrently.
A power allocation controller is generally configured for a particular fixed allocation limit by connecting resistors or other components to programming inputs on the power allocation controller. However, if alternate adapters requiring different allocation limits are available to be coupled to an electronic device, for example a lightweight travel adapter with a small maximum power rating and a larger docking station adapter or fast-charge adapter with a higher maximum power rating, the power allocation controller in the electronic device will be unable to adjust its operation to the allocation limit associated with each alternate adapter, using instead the fixed allocation limit set at the time the electronic device was manufactured. Mismatched allocation limits raise the possibility that battery charging will not proceed at a desired rate or that the maximum adapter power may be exceeded by the electronic device. An example of power allocation control with a fixed power allocation limit is provided in U.S. Pat. No. 6,611,129.
Other efforts have been directed at passing one or more fixed values relating to adapter specifications such as maximum current or maximum power from an adapter to an electronic device modified to receive the values. An electronic device modified to receive fixed values related to adapter parameters can determine how much adapter output current to allocate between battery charging circuits and active systems or make other decisions about operating modes for the electronic device. In one exemplary power supply circuit, an electronic device receives information about an adapter but does not use the information to modify the adapter's output voltage, that is, there is no closed-loop control of adapter output voltage by the electronic device. Without closed-loop control of adapter output voltage, the necessity for a large difference between adapter output voltage and battery voltage remains, leading to lower power efficiency as earlier described. An example is provided in U.S. Pat. No. 6,058,034.